1. Field of the Invention
The present invention relates to a wireless communication apparatus and the receiving control method thereof.
2. Description of the Related Art
Generally, in a digital cellular phone, the improvement in time resolution in a BB (baseband) signal process and the reduction of the number of components are targeted, and as shown in FIG. 13, a master clock used in the BB process is supplied from a TCXO (temperature compensation crystal oscillator) 1401, which is the reference frequency oscillator of a wireless processing unit 1400.
Since during normal communications in this system, clock jitters in the BB signal process are reduced, transmitting and receiving performance is improved.
However, also during intermittent receiving standby, a reference clock oscillator 1403 requiring relatively large current has been operated, and the timing control of intermittent reception has been exercised using a high-accuracy clock signal as a reference frequency.
FIG. 1 outlines the use mode of a clock signal of a conventional cellular phone.
First, the wireless processing unit 1400 reproduces the carrier of a received signal, and converts the RF (Radio Frequency) signal to an IF (Intermediate Frequency) band or baseband signal. In this configuration, since no sufficiently accurate reproduction of the carrier causes a great degradation in the amplitude of the IF band or baseband signal, the reproduction of the carrier is performed using a clock signal generated by the highest-accuracy TCXO 1401 as a master clock signal.
However, a timing process unit 1402 extracts binary-coded data from the amplitude of the baseband signal converted by the wireless processing unit 1400. The timing process unit 1402 is operated in two ways: in one way, the frequency of a clock signal from the TCXO 1401 is divided and one of the divided frequencies is used to operate the timing process unit 1402, and in the other way, a reference clock signal (reference clock oscillating circuit) 1403 is provided in addition to the TCXO 1401 and the timing process unit 1402 is operated using the reference frequency. If the timing process unit 1402 is operated by using the divided frequency of a clock signal of the TCXO 1401, the TCXO 1401 must be driven even when there are no actual communications. In this case, since the TCXO 1401 has a high accuracy and requires a large amount of power, the power is wasted if the TCXO 1401 is operated during receiving standby (period in which no signals are being received, but an apparatus is ready to receive signals at any time). For this reason, in some conventional cellular phones, the operation of the TCXO 1401 is stopped during receiving standby, and the timing process unit 1402 is driven -using the reference clock signal 1402 separately provided and which has a lower accuracy, but requires a smaller amount of power than the TCXO 1401.
An MMI (Man-Machine Interface) unit 1404 displays characters on the display of a cellular phone, and is driven by a time clock signal (time clock oscillating circuit) 1405 which has a lower accuracy than both the TCXO 1401 and reference clock signal 1403. Since this MMI unit 1404 must also always be ready to respond to a user operation and display the time on the display, the MMI unit 1404 is driven by the time clock oscillating circuit 1405 which is always operated. Since the time clock signal 1405 has a lower accuracy than both the TCXO 1401 and reference clock signal 1403, but the smallest power consumption of the three units, the receiving standby time of a cellular phone is not reduced even if the time clock oscillating circuit 1405 is always operated.
Regardless of a system, such as a PHS (Personal Handyphone System), PDC (Personal Digital Cellular) system, CDMA (Code Division Multiple Access) system, etc., a large burden is imposed on the receiving standby time in a performance comparison between cellular phones.
However, since weight/size is also a major factor in the performance comparison between cellular phones, receiving standby time cannot be freely increased by increasing the battery capacity.
In a TDMA (Time Division Multiple Access) system, the higher the accuracy of the reference clock signal 1403 during a BB signal process, the more the frequency at which jitters occur is reduced during BTR (reproduction of a receiving clock signal). Therefore, the TDMA system has a theoretical advantage over other systems in transmitting and receiving characteristics. Since the adoption of a reference clock signal 1403 has a certain degree of an effect on the improvement in performance regardless of the fluctuation in performance of components, etc., the adoption of a reference clock signal is a very effective means for improving the overall performance of mass-produced cellular phones.
If a reference clock oscillating circuit 1403 is provided separately, the receiving characteristic can be improved. However, in this case, the reference clock oscillating circuit 1403 requires a larger amount of power than a time clock oscillating circuit 1405. Thus, a cellular phone which consumes a small amount of power and has a long receiving standby time is desired.
An object of the present invention is to provide a cellular phone with a configuration to reduce the power consumption during intermittent receiving standby.
The receiving control apparatus of the present invention comprises a reference frequency oscillator (TCXO) for generating a first high-accuracy clock signal, a time clock oscillator for generating a second clock signal which has a lower accuracy than a clock signal generated by the reference frequency oscillator, with smaller power consumption than the reference frequency oscillator, a receiving unit for receiving transmitted signals and a control unit for controlling the apparatus so as to receive signals by driving the receiving unit based on the first signal generated by the reference frequency oscillator during normal communications, so as to stop the master clock unit and to manage/control intermittent receiving timing based on the second clock signal generated by the time clock signal during receiving standby, so as to start the reference frequency oscillator based on the second clock signal generated by the time clock oscillator when the apparatus shifts from a receiving standby state to a communications state, and to make the receiving unit start receiving signals after the operation of the reference frequency oscillator is stabilized.
The receiving control method of the present invention comprises the steps of (a) generating a first high-accuracy clock signal, (b) generating a second clock signal which has a lower accuracy than the clock signal generated in step (a), with smaller power consumption than that used in step (a), (c) receiving transmitted signals, and (d) controlling the apparatus so as to receive signals in step (c) based on the first clock signal generated in step (a) during normal communications, so as to stop the generation of the first clock signal in step (a) and to manage/control intermittent receiving timing based on the second clock signal generated in step (b) during receiving standby, so as to start the process in step (a) based on the second clock signal generated in step (b) when the apparatus shifts from a receiving standby state to a communications state, and so as to start the reception of signals in step (c) after the operation in step (a) is stabilized.
According to the present invention, since during receiving standby only the time clock oscillator is operated and the reference frequency oscillator for outputting a high-accuracy clock signal is not operated, the power consumption can be reduced. When data are received, the signal accuracy the same as that in the case where signals are received while the reference frequency oscillator is operated, can be received since the reference frequency oscillator is started based on the count value of the second clock signal outputted from the time clock signal and signals are received based on the high-accuracy clock signal generated by the reference frequency oscillator prior to reception.
In another aspect of the present invention, the apparatus comprises means for storing both the detected value of the frequency deviation against the first clock signal generated by the reference frequency oscillator of the second clock signal generated by the time clock oscillator and the phase difference value between a receiving clock signal extracted by the received data and the second clock signal generated by the time clock oscillator, and timing started by the reference frequency oscillator is adjusted taking into consideration the stored frequency deviation and phase difference. Therefore, the correct reception of data can be guaranteed and the apparatus can be controlled in such a way that the power is not wasted by starting the reference frequency oscillator too early.